mpi: harden add_n_cond, sub_n_cond and abs_cond against EM leakage
9bc3d8de6e2a
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mpi: harden add_n_cond, sub_n_cond and abs_cond against EM leakage

* mpi/mpih-const-time.c (_gcry_mpih_add_n_cond)
(_gcry_mpih_sub_n_cond): Always perform calculation with both UP and
VP; Use two masks for selecting output.
(_gcry_mpih_abs_cond): Always calculate absolute value of UP; Use
two masks for selecting output.

GnuPG-bug-id: T5330
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>